Maintenance Guide: Compressed Air Systems - Dryers, Filters and Leak Audit

1. Scope and Objective

This technical guide provides preventive and corrective maintenance procedures for industrial compressed air handling systems, specifically dryers (refrigeration and adsorption), filtration stages (pre-filters, coalescence filters, submicron particulate filters) and leak detection audit methods. The objective is to ensure the supply of quality compressed air that complies with the requirements of the ISO 8573-1:2010 standard (purity classes) and sectoral standards, particularly for applications in aeronautics and energy which require air free of contaminants and humidity. Regular maintenance is essential to maintain system energy efficiency, prevent corrosion of downstream equipment, reduce unplanned downtime, and extend the life of pneumatic components.

2. Safety Precautions

WARNING: Safety is critical when working on pressure systems. Failure to follow procedures could result in serious injury, death, or significant property damage.

• Lockout/Tagout: Before any intervention, isolate the system from any source of energy (electrical, pneumatic) and lock it out in accordance with standard NF C18-510. Check the absence of tension and the absence of residual pressure.
• Depressurization: Always completely depressurize the compressed air circuit by opening the purge valves and checking the pressure gauge display before loosening fittings or opening casings. The rated operating pressure can reach 10 bar, representing a high risk.
• Personal Protective Equipment (PPE): Always wear protective glasses (EN 166), protective gloves (EN 388), safety shoes (EN ISO 20345) and, if necessary, hearing protection (EN 352) during ultrasonic leak audits or near purges.
• Hot Surfaces: Refrigeration dryers can have hot surfaces (exchangers, refrigeration compressors). Use an infrared thermometer before contact and wear thermal gloves if necessary.
• Condensates and Oils: Condensates may contain water, oil and other contaminants. Collect and dispose of these fluids according to local environmental regulations. Avoid prolonged skin contact.
• Treatment Products: Desiccants (silica gel, molecular sieve) can be irritating. Handle with gloves and protective glasses. Consult specific safety data sheets (SDS).

3. Tools and Materials Required

4. Pre-Maintenance Inspection Checklist

5. Walkthrough

5.1. Initial Preparation and Safety

1. Isolate and Record:
   • Turn off electrical power to the air compressor and air handling system (dryer, filters) at the main circuit breaker.
   • Apply the lockout/delockout (LOTO) procedure by attaching padlocks and labels to energy isolation devices. Never skip this step, even for a quick intervention.
2. Depressurize the System:
   • Close the shut-off valve located upstream of the dryer and filters.
   • Slowly open the manual purge valve closest to the intervention area to release residual compressed air.
   • Check that all pressure gauges indicate 0 bar. Ensure that the pressure is completely released before opening any component.
3. Collect the Condensates:
   • Place the retention tank under the automatic and manual drains, as well as under the filter housings.
   • Open the automatic drains in manual mode if possible to empty the water separators.

5.2. Compressed Air Dryer Maintenance

5.2.1. Refrigeration Dryers

1. Cleaning the Exchangers:
   • Using a soft brush and a vacuum cleaner, clean the fins of the air-air exchanger and the evaporator to remove dust and debris. Do not use a metal brush which could damage the fins.
   • Check for obstruction of cooling air flow.
2. Checking the Refrigerant Circuit:
   • Visually inspect the refrigerant pipes for traces of oil or frost, which could indicate a leak.
   • Check the refrigerant level through the viewing window (if present); low level or excessive bubbles suggest a leak.
   • Check the operation of the pressure switch and the refrigeration circuit thermostat.
3. Checking the Condensate Drains:
   • Clean the automatic drain mechanism (mechanical or electronic).
   • Test manual operation to ensure they open and close properly without continued air leaking after closing.

5.2.2. Adsorption Dryers (Desiccants)

1. Desiccant Inspection:
   • Open the inspection ports of the adsorption towers (if present) or take a desiccant sample. Make sure the tower is completely depressurized.
   • Check the color of the desiccant (for colored silica gel) and the physical integrity of the beads (absence of spraying or agglomeration).
   • If the desiccant is saturated, pulverized or caked, replace it completely.
2. Replacing the Desiccant (if necessary):
   • Drain the tower of its used desiccant into a suitable container.
   • Fill the tower with new desiccant (silica gel or molecular sieve) to the volume and type specified by the manufacturer. Close the opening with a tightening torque of 30-40 Nm for 100 mm flanges.
   • Make sure the desiccant is evenly distributed.
3. Checking Switching Valves:
   • Visually inspect the condition of the plug or seat valves (often pneumatic or electric) that control airflow between towers.
   • Test their operation if the system allows a manual or visual cycle (without pressure). Ensure complete and rapid switching.
4. Purge Flow Check:
   • Check that the purge air flow (required for regeneration) complies with the manufacturer's specifications. Excessive flow wastes energy, insufficient flow compromises regeneration.
   • Adjust the purge flow control valve if necessary.

5.3. Replacement of Filter Elements

1. Isolate and Depressurize:
   • Follow steps 5.1.1 and 5.1.2 for the insulation and depressurization of the compressed air lines before the filters to intervene.
2. Open the Filter Housing:
   • Loosen the screws or the filter housing clamp. Use a torque wrench for the screws, if specified by the manufacturer. For a standard G1/2 filter housing, a torque of 20 Nm is typical for the fixing screws. For a large G2 crankcase, a torque of 40-50 Nm may be required.
   • Remove the housing carefully, paying attention to residual condensate.
3. Replace the Filter Element:
   • Remove the old filter element by pulling or unscrewing it (depending on the type).
   • Inspect the inside of the crankcase for signs of corrosion, excessive fouling or damage. Clean if necessary.
   • Replace all O-rings on the housing and filter element with new ones, lubricated with a thin layer of compressed air compatible silicone grease. Never reuse old O-rings.
   • Insert the new filter element ensuring it is properly engaged and sealed in the housing.
4. Close the Filter Housing:
   • Replace the filter housing and tighten the screws or the clamp. Respect the tightening torque specified by the manufacturer (for example, 20 Nm for M8 screw, 45 Nm for DN50 collar).
   • Tighten the screws progressively and crosswise to ensure uniform pressure distribution.

5.4. Leak Detection Audit

1. Preparation:
   • Ensure that the compressed air system is under its normal operating pressure (eg: 7 bar).
   • Minimize ambient noise as much as possible (turn off non-critical machines).
2. Using the Ultrasonic Detector:
   • Turn on the ultrasonic leak detector and adjust the sensitivity.
   • Systematically go through all piping, fittings, valves, quick connects, hoses, cylinders and pneumatic equipment. The effective range is generally 1 to 5 meters.
   • A leak generates a characteristic sound (hissing) converted into a frequency audible by the device. The location is precise and visual (intensity indicator).
   • Mark each leak detected with a label or permanent marker, noting its location and an estimate of its size. Do not underestimate small leaks, their accumulation can be significant.
3. Soapy Solution Method (for confirmation or small leaks):
   • Apply the soapy solution to suspect areas (connections, welds, joints).
   • The appearance of visible bubbles confirms the presence of a leak.
4. Pressure Drop Audit (for overall assessment):
   • After production hours, isolate a section of the compressed air network or the entire system downstream of the compressor.
   • Note the initial pressure.
   • Wait a defined period (eg: 15-30 minutes) and record the final pressure.
   • Calculate the pressure loss. A loss greater than 0.5 bar over 30 minutes is an indicator of significant leaks requiring immediate action.
   • This method is complementary and makes it possible to assess the overall extent of the problem.
5. Reporting and Prioritization:
   • Document all leaks found, their location, estimated severity and recommended corrective action.
   • Prioritize repairs based on impact on energy efficiency and production.

6. Post-Maintenance Verification Checklist

7. Troubleshooting Guide

8. Recommended Maintenance Schedule

9. Spare Parts Reference

For any spare parts or consumables, please consult our online catalog: https://www.unitecd.com/e-catalog/

10. References

• NF EN ISO 8573-1:2010 standard: Compressed air — Part 1: Pollutants and purity classes.
• NF standard EN 12021:2014: Respiratory equipment — Compressed air for respiratory protection devices.
• Standard NF C18-510: Operations on electrical works and installations or in their vicinity – Prevention of electrical risks.
• AFNOR FD E 58-100 Guide: Recommendations for the installation of compressed air networks.
• OEM (Original Equipment Manufacturer) technical documentation specific to each model of dryer and filters.
• Machinery directives 2006/42/EC (CE marking).
• ATEX 2014/34/EU directive (if application in potentially explosive areas).